Oscillation generator including a cathode-ray tube



April 1947. M. J. o. STRUTT ET AL OSCILLATION GENERATOR INCLUDING A GATHODE RAY TUBE Filed March 23,. 1945 2 Sheets-Sheet l INVENTORS MAX/M/L/AAN J. 0. smurf ALBERT Vyfk Z/EL ATTORNEY ?atented Apr. 8, 1947 OSCILLATION GENERATOR INCLUDING A CATHODE-RAY TUBE Maximiliaan Julius Otto Strutt and Aldert van der Ziel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn.,'as trustee Application March 23, 1943, Serial No. 480,195

In the Netherlands July 11,. 1940 i 4 v 7- Claims.

This invention relates to oscillation generators of the type having a cathode ray tube wherein the frequency of the oscillations generated is a function of the cyclic rate of deflection of the electron beam; the frequency being also dependent upon the rateat which the electron beam is caused to sweep across a succession of target anode surfaces and to penetrate a plurality of apertures between said surfaces. Although, in perfecting our invention, we have adopted certain well known features of cathode ray tube generators, we have, nevertheless, contributed materially to the useful scope of such devices by providing a novel construction of cavity resonator within the envelope of the cathode ray tube.

In our system a current impulse is produced in an output circuit connected to the receiving electrode in each instance when the receiving electrode is struck by the beam, the frequency of said impulses being determined by the product of the frequency of the controlling oscillation and the number of apertures over which the beam is passed during one cycle of'the controlling oscillation. The output circuit is made to oscillate by the current impulses and is tuned to the frequency of the current impulses. To obtain a high power output oscillation the output circuit should present a high impedance to this frequency.

In devices of the said kind hitherto known for generating oscillations having a wave length of several decimeters difficulties were experienced in the construction of an output circuit presenting a sufiicient impedance to the oscillations to be generated.

According to the invention these difficulties are obviated by making use of a device in which two of the apertured electrodes or one of these electrodes and the receiving electrode are united to form a hollow member which constitutes a res-' onant circuit tuned to the frequency of the oscillations to be generated.

The invention will be more fully explained by reference to the accompanying drawing forming a part of the specification and in which:

Fig. 1 is a diagram partially in section and partially schematic illustrating adevice according to the invention.

Fig. 2 is a plan view of a component part of the device illustrated in Fig. 1.

Fig. 3 is a diagram of another device according to the invention.

.Eig. 4 is a diagramv illustrating. a further embodiment of the invention.

.Fig. 5 isa plan view ofan alternate component 2 part. of the devices illustrated in the foregoing figures and Fig. 6 is a diagram illustrating still another device according to the invention.

The device shown in Fig. 1 comprisesa cathode ray tube furnished with, the usual means for generating a beam of electrons. thesame means consisting of a cathode I a control electrode 3 and an accelerating electrode 5. The tube is represented in axial section. To concentrate the beam there may be provided a focussing coil I energized by direct current together with amagnetic screen 8 by which the deflecting means of the tube are withdrawn from the influence of the field of coil 7. The deflecting means of the I tube consist of a set of deflecting plates 9 which are connected to the end of a resonant circuit which is represented in Fig. 1 by a capacity ii and an inductance coil [3 which coil is coupled to a coupling coil l5. At the other end of the tube there are provided, coaxially with the device described hereinbefore, an apertured electrode I! and a receiving electrode i9 which, as; will be explained more in detail hereinafter, are united according to the invention to form a hollow member 2| by means of an annular metal box 23, which member is completely closed except for an annular aperture 25 in the electrode H. Within the hollow member 2| a grid 27 whichextends normally to the axis is located about mid-way between the electrodes I! and Is. This grid is connected for high frequencies through a condenser 30' to the box 23' and is earthed for high frequencies across a condenser 29. The electrode i9 is connected to the outer conductor 3|, the electrode I! being connected to the interior conductor 33 of' a concentric transmission line 3|, 33 which at the other end is connected to a load circuit, for instance, an antenna 35. From a source of direct current, for instance, a battery 4|, suitable positive voltages relatively tothe cathode I are supplied to the electrode 5 and the member 2!, the electrode 3 receiving a negative voltage through a secondary winding 45. of a transformer 43, 45.

The device I, 3', 5 produces a beam of electrons, indicated by a dotted line 2, which beam can be concentrated by the focussing coil 7. To the oscillatory circuit H, l3 connected to the deflecting plates 9 a high frequency controlling voltage is supplied through the coupling coil I5 whereby the beam is caused to travel to and fro, the point at which the beam hits the electrode t1 travelling over this electrode between two extreme points Pand Q. .As appears from Fig. 2, which is a front view of the member 2|, four times a group of electrons of the beam falls through the annular aperture 25 on the electrode I9, per to and fro motion of the beam that is, per cycle of the controlling oscillation supplied to the electrodes 9. During the travel of such a group of electrons from the electrode I! to the electrode IS a curconstitutes the tuning capacity, the tuning inductance being mainly constituted by the electrodes l1 and IS. The resonant circuit thus constituted serves as an external circuit between the electrodes i1 and I9 and is made to oscillate by the current impulses occurring between these electrodes; the frequency of the generated oscillation is the same as that of the current impulses, in the case referred to, consequently the four-fold frequency of the controlling oscillation.

When making use of the step to be taken according to the invention a resonant circuit is formed which is connected between the electrodes l1 and I9 and which even at very high frequencies exhibits very small losses, and hence a high impedance as a result of which a considerable output energy is obtainable. The high degree of freedom of loss of the circuit l1, I9, 23 is a result of the very small losses in the inductance constituted by the connection between the electrodes l1 and I9. This connection is constituted by a single turn having a large surface owing to which the loss resistance for high frequency currents is small. Moreover, the magnetic flux is closed in itself and extends entirely within the member 2|. Leakage fields liable to strike metal parts and causing losses are thus avoided. Moreover, connecting lines are superfluous, since the electrodes l1 and |9 form themselves part of the resonant circuit.

From experiments and also upon calculation it appears that for suitable operation the distance between electrodes "and i3, taking into account the velocity of the electrons, must be so chosen that the transit time of an electron between the electrodes l1 and I9 is less than half a cycle of the output oscillation. This means that the distance between electrodes l1 and I9 will generally be very small. To ensure that the connection through which these electrodes are united to form a hollow member has a considerable inductance, the connection is preferably constituted by an annular metal box 23 which extends coaxially with the electrode l1 and I9 and whose diameter and axial length is larger than the diameter and distance between the electrodes H and |9 respectively.

The ends of the resonant circuit constituted by the hollow member 2| are located in the center of the electrodes I1 and I9 respectively. The oscillatory energy available in the circuit may be supplied to a load circuit. for instance, to the antenna '35, through the intermediary of the transmission line 3|, 33 whose two conductors are connected respectively to the said centers.

The transit time of the electrons between the electrodes l1 and I9 is determined by their average velocity and by the distancebetween these electrodes. The electrons enter the member 2| at a deiinite initial. speed and are slowed down therein due to the fact that they cede energy.

After having traversed the member 2| in an axial direction the electrons hit the electrode l9, it being possible that secondary electrons are dislodged which travel to the electrode By these electrons a current impulse from the electrode 59 to the electrode IT is produced in the output circuit, which impulse is opposite to that producing the output oscillation and consequently counteracts the latter. Therefore, according to the invention, the receiving electrode l9 preferably has no or only a small secondary emission, since it is coated, for instance, with a layer of soot at least on the side where the electrons are received.

In order to prevent secondary electrons dislodged irom the electrode Hi from reaching the electrode ll, according to the invention, the grid 21, which is preferably earthed for high frequencies across a condenser 29, is located about mid-way between the electrodes I1 and |9 and parallel therewith, which grid repels any secondary electrons issuing from the electrode IS. The grid 2'! is connected for high frequencies through the condenser 30 to the middle of the mantle of the box 23. The center of the resonant circuit constituted by the member 2| is consequently earthed for high frequencies across condensers 29 and 39.

The grid 21 also has another-function. During one-half of the cycle of the output oscillation the electrode i9 is negative with respect to the electrode l'l. In the absence of a grid 21 a group of electrons staying in front of the aperture 25 during this half cycle is attracted by the electrode H and repelled by the electrode |9 so that the electrons are likely to be scattered and instead of passing through the aperture 25 to the electrode l9 travel to the electrode By providing the grid 21 the risk thereof is greatly reduced, because during the said half cycle the negative voltage of the grid 21 with respect to the electrode i1 is only half that of the electrode l9, since the grid 21 is connected for high frequencies to a mid-tap of the circuit l1, I9, 23.

Instead of an annular aperture the electrode I! may exhibit two slit-shaped apertures 25 through which the beam of electrons passes alternately. According to the invention, however, an annular aperture is preferably used. In fact, the line PQ along which travels the point where the beam hits the electrode 1'! tends to turn about the axis of the cathode ray tube and to occup for instance, the postion P'Q'. As a result of the annular shape of the aperture 25 the distance between the points where the beam passes through the electrode I1 is always the same, it being thus ensured that the current impulses relatively to one another always occur at the correct moments as long as the deflection of the beam of electrons under the action of the controlling voltage, that is, the length of line PQ, remains the same.

The device represented in Fig. 1 is also adapted for generating modulated oscillations. For this purpose a modulating voltage is supplied to the primary winding 43 of transformer 43, 45, The modulating voltage induced in the secondary winding 45 of this transformer is supplied to the control electrode 3 and causes intensity variations of the beam of electrons, which correspond to the modulating voltage and as a result of which the maximum amplitude of the output oscillation is varied proportionally to the momentary amplitude of the modulating voltage.

Fig. 3 represents partly in section, and partly in perspective another form of; construction 0. the device according tothe invention.. Thi form-of construction substantially -,corresponds to thatshown in Fig. l butit comprises ;-a device of "the beam is effected by the. electrodes fi-which serve as deflecting plates at the same time; tothisend they are connected, in the-manner shown already in Fig. 1, to-a resonant circuit H, H; and

via thecenter of coil 13a positive auxiliaryvoltage is supplied from the battery 4! to the-two plates. The operation corresponds to'that of the device-shown in Fig. 1.

Figs 4 and 5 represent another; form of-"construction of the device according to the invention. by means of which anoutput-oscillation can be obtained whose frequency amounts to many times that of the controllingoscillation. Fig. 4.;largely corresponds to Fig. 1. However, thedevicevshown in Fig. 4 comprises another set of deflectingplates l0 which extend normally to the plates 9; The plates W are connectedto a resonant circuit represented by a condenser l2 anda coil I 4. The coil -l4-is-coupled to a coupling coil It towhich, as well as to coil l5, the controlling oscillation is supplied; The circuits l I, I3 and I2, I 4 are slightly detuned relatively to one another so that the alternating voltages occuring acrossthe cir cults differ in phase by 90. Thus a rotary electric field is set up between the deflecting plates 9 and Ill as a result of which the'beam acquires a rotary. movement about its original direction as an axis, Owing to this movement th beam is made to follow a circular path overthe electrode l1 which electrode in the present form of construction. of the device, according; to the invention, is shaped as shown in Fig. 5, viewed the direction oftravel of the electrons. The electrode l1 exhibits a number of apertures zfi located along the periphery of a circle. The amplitudes of the alternating voltage occurring between the deflecting plates 9 and M! respectivel are adjusted so that the beam passes over the apertures 26 and alternately hits the electrode l! and, through one of the apertures 26. the electrode Hi, the current impulses produced in the manner set out above exciting the resonant circuit constituted by the hollow member 2!. The beam performs one revolution per cycle of the controlling oscillation, the number of current impulses produced corresponding to the number of apertures 26. Consequently, the number of current impulses per second, i. e., the frequency of the output oscillat on corresponds to the frequency of the controlling oscillation multiplied by the number of apertures 25. At variance with Fig. 1 the output energy in the device shown in Fig. 4 is taken from the resonant circuit ll, 23, 19 by means of a loop 3! which is led in an insulated manner through the Wall of box 23, this loop being coupled to the magnetic flux of the circuit and connected to two output terminals 39 outside of the member 2]. However, use may also be made of the device bearing the reference numbers 3 l, 33, 35 in Fig. 1.

Fig. 6 represents one embodiment of the invention which substantially corresponds to that shown in Fig. 4, but which comprises more than one apertured electrode in such manner that corresponding apertures ofthe succeeding electrodes in the direction ofthe-beam of electrons are in line; with; oneanother; According to the invention-there are provided three apertured electrodes 'l,- l8 and; I 9; In the present form ofconstruchigh frequencies through a condenser 52,- the electrodes land 28 being earthed for the frequency ofthe-output oscillation bymeans of condensers-, 53 and elirespectively. The D. C. voltag pplied to thehollow member 5 amounts to several; times the voltage supplied to the electrodes it and; 20 ;the said voltages may amount, for instance, to 5600, volts and 500 volts respec: ti-vely The; electrons from the beam 2 are alternately intercepted by the electrodes l8 and Eli. Since 'these electrodes have a comparatively low D. C. voltage and no alternating voltage, little energy is. lost so that a satisfactory efficiency can be obtained. The electrodes IT- and 99 are not hit by electrons, so that there does not flow direct current to these electrodes.

As has already been set out, the distance between the electrodes, H and I9 is preferably chosen so that the transit time of the electrons between the said electrodes amounts at most to half a cycle of the output oscillation. The distance betwen the electrodes is and El and between the electrodes 59 and 25 may be much larger; thedistance betwen the electrodes l9 and 20. is preferably chosen so that a space charge accumulates betwen them, which results in that any secondary electrons dislodged from the electrode 2!! return to this electrode.

We claim:

1. An electronic device comprising an evacuated envelope containing an electron gun for emitting a focused electron beam, deflecting means along the trajectory of said gun for periodically deflecting said beam, a metallic shell constituting a cavity resonator and having two opposed walls which are spaced apart in accordance with a functional requirement concerning the transit time of electrons passable therebetween, a suppressor grid electrode substantially midway between and lying in a plane parallel to said opposed walls of said cavity resonator, said shell having a peripheral wall constituting a metallic connection between said two Opposed walls, one of said opposed walls having apertures in registry with said trajectory for the intermittent entry into said cavity resonator of electrons emitted by said gun, and an output circuit comprising two conductors individually connected to each of said opposed walls.

2. An electronic device comprising an evacuated envelope containing an electron gun for emitting a focused electron beam, deflecting means along the trajectory of said gun for periodically deflecting said beam. a metallic shell constituting a cavity resonator and having two opposed disc wall portions which are spaced apart in accordance with a functional requirement concerning the transit time of electrons passable therebetween and two opposed annular wall portions exterior to the circumference of said disc wall portions, said annular wall portions being spaced farther apart than said disc wall portions and having a peripheral wall constituting a metallic connection between said two opposed annular wall portions, one of said opposed disc wall portions having apertures in registry with said trajectory for the intermittent entry into said cavity resonator of electrons emitted by said gun, and an output circuit comprising two conductors individually connected to each of said two opposed disc wall portions.

3. An electronic device comprising an evacuated envelope containing an electron gun for emitting a focused electron beam, deflecting means along the trajectory of said gun for periodically deflecting said beam, a metallic shell constituting a cavity resonator and having two opposed walls which are spaced apart in accordance with a functional requirement concerning the transit time of electrons passable therebetween, said shell having a peripheral wall constitutin a metallic connection between said two opposed walls, an electrode having apertures interposed between said electron gun and said metallic shell, each of said opposed walls having apertures, the apertures of said electrode and said walls being in registry with said trajectory thereby permitting said electron beam to penetrate corresponding apertures in a straight path, and an output circuit comprising two conductors individually connected to each of said two opposed walls.

4. An oscillation generator comprising a cavity resonator having an apertured conductive shell, an output coupling connected to said shell, electrode plates external to said shell and disposed in capacitively reactive relation thereto, one of said plates having apertures in alignment with those of said shell, and excitation means for said resonator comprising an electron beam projector having a trajectory registry with said apertures, and beam deflecting means disposed along said trajectory for directing a fiow of electrons through the apertures of said plate and of said shell.

5. A cathode ray tube having an electron gun for emitting an electron beam, a cavity resonator having both inner and outer electrode surfaces disposed in the path of the electron beam, said electrode surfaces including two opposed flat portions both normal to the axis of said beam, but

one only of which is apertured, namely, the portion which faces said gun, deflecting means disposed along the trajectory of said gun for periodicaliy deflecting electrons of said beam as they travel toward said cavity resonator, said resonator constituting means for causing oscillations to be generated at a frequency which is high relative to the oscillatory rate of deflection of said electron beam.

6. A cathode ray tube in accordance with claim 5 and including a suppressor grid mounted within said cavity resonator.

7. An ultra high frequency generator comprising a cathode ray tube having an electron gun and beam deflecting means disposed along the trajectory of said gun, a cavity resonator comprising a system of target electrodes, one of which, facing the gun, has apertures, a substantially toroidal envelope interconnecting said target electrodes, and means including a suppressor grid electrode situated within said cavity resonator for controlling the flow of secondary electrons between one and the other of said target electrodes.

MAIGMILIAAN JULIUS OTTO S'IRUT'I. ALDERT VAN DER ZIEL.

REFERENCES CITED The following references are of record in the file of this patent:.

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